Switches are used in industrial plant and automation systems but also in the consumer area. They function not only as pure command devices employed to change the status of a machine, a computer or similar, but are also used for interaction between human and machine. They can therefore also be counted as input/output devices in the sense of a Human-Machine Interface (HMI). The feedback to the operator is realized via an optical display which has an information content which is directly related to the machine or to its operating states or switching states. Rotary switches, lever switches, rocker switches, slider switches or push switches/buttons should be mentioned as examples at this point.
The optical display can be based in this case of different methods for visualizing information. Essentially a distinction is made between electrical and mechanical switches. The electrical displays are primarily equipped with light emitting diodes (LEDs) or incandescent lamps. The spatial extent of the electrical lighting elements presents a problem as these elements then occupy valuable space in a switch which is not available to the switching mechanism of the switch. Mechanical displays which can have at least one movable element which appears or disappears in a window represent a further option. Command devices or switches, such as an emergency shutoff switch with a signal display for example, are more susceptible to faults and have a shorter life purely because of their additional mechanics.
Mechanical and electrical displays typically feature symbols and/or text characters for example which are attached to the respective display element or are formed by the latter.
An electrical switch with an illuminated display which is based on a light emitting diode to illuminate its functions is known from DE 43 05 349 A1.
Further, in recent years so called electrochromic displays have been developed in conjunction with other technical challenges. The functioning of an electrochromic display can be illustrated with reference to the exploded diagram shown in FIG. 1.
The main component of the electrochromic display is the electrochromic material 3 which is arranged between lower electrodes 1.1, 1.2, 1.3 and upper electrodes 2.1, 2.2, 2.3. By applying a voltage via an upper and a lower electrode, an area of the electrochromic material 3 can be energized. The consequence of applying an electrical potential is that the optical properties, such as the absorption or reflection behavior for example, are changed. In this case the electrochromic material 3 itself represents an electrochromically reactive layer. The application of an electrical potential appears to the human eye as a change in contrast or in color.
The upper electrodes 2.1, 2.2, 2.3 can in this case be embodied as transparent electrodes which are protected from environmental influences by a protective layer 6.
The electrochromic display from FIG. 1 has a matrix control which allows the electrochromically-reactive layer to be controlled pixel-by-pixel. The lower electrode 1.2 and the upper electrode 2.3 are set by the voltage source 5 to different potentials so that the area 4 (pixels) changes its reflection or absorption properties and delivers to the user a part of the information to be transferred. Such matrix controls are known from LCD or OLED displays for example.
Although the electrochromic display is applied on a carrier layer 7 it is typically 250 micrometers in width.
An electrochromic component, a so-called “smart window”, is known from WO 2004/081644 A1, in which the color behavior of an EC material is controlled by the application of a voltage to the electrodes.